The event-related desynchronization/synchronization (ERD/ERS) were determined using the method of complex demodulation with a simultaneous signal envelope computation (Andrev, 1999; Otnes and Enochson, 1978 and Thatcher et al., 1994). In this method the raw data for each channel are multiplied, point by point, by a pure cosine based on the selected center frequency, as well as by a pure sine having the same center frequency. Both time series (multiplied by a pure sine and cosine) are then lowpass filtered by the half-bandwidth (1 Hz for the α frequency bands, and 9 Hz for the γ band).
The quantification of induced ERD was done using the intertrial variance method (induced, non-phase-locked activity). The formulas used were as follows